The most important advantage of using liquid lead as coolant for a nuclear reactor is that it allows designing the reactor in a highly compact format, with an outstanding set of safety features, including:
• No violent exothermic reaction with water
• A very high boiling temperature, reducing the risk for loss of coolant
• An excellent potential for decay heat removal by natural convection
• Chemical retention of iodine and caesium, should a fuel failure occur
• Inherent shielding of gamma radiation from fission products
Moreover, the use of lead as coolant results in a so called "fast" neutron spectrum, which facilitates production of fissile fuel from U-238 with a conversion ratio larger than unity. Hence, fuel resources increase by two orders of magnitude, making nuclear power sustainable for thousands of years. Moreover, the fast neutron spectrum makes it possible to efficiently transmute the long-lived waste, such as americium and curium, into stable or short-lived fission products, with a minimum of negative side-effects on the safety of reactor and fuel-cycle facilities.
A major disadvantage of using lead coolants is the risk for corrosion attack on fuel cladding and steam generator tubes. The high solubility of nickel in lead makes it necessary to form and maintain a protective oxide film on the surfaces of structural materials. However, chromium oxide scales forming on conventional stainless steels grow too thick after a year of full power operation in a lead-cooled reactor, making them mechanically unstable. Silicon or aluminium alloyed steels form thinner films of silicon and aluminium oxides, respectively, rendering the steels corrosion proof over longer exposure times. In Russia, a silicon alloyed steel has been developed for use in the SVBR-100 and BEST-300 reactors, whereas in Germany, a technique for surface alloying of steels with FeCrAlY has allowed to improve corrosion and fretting performance significantly.
In collaboration with Swedish steel industry, LeadCold materials experts have developed an aluminium alloyed steel (Fe-10Cr-4Al-RE) which exhibits perfect corrosion resistance during exposure to lead for more than two years at T = 550°C, and for more than 10 weeks at 850°C. The addition of reactive elements (RE) reduces the risk for formation of chromium carbides that may be detrimental for corrosion resistance, and allows to keep the aluminium concentration at a level low enough to ensure weldability of the material. Based on this break-through innovation, LeadCold has designed the SEALER reactor for commercial power production.
The peer-reviewed publications listed below contain scientific substantiation for the design of lead-cooled reactors and the technology to be applied in SEALER:
Fe-Cr-Al-RE alloy exposed to lead for 19 000 hours at 550°C
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